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(11) | EP 0 239 164 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Battery comprising one or more electrochemical cells having a negative electrode of an alkali metal |
| (57) A battery of one or more electrochemical cells comprises in a metal cell box having
a metal double-walled cell lid (2) with a leadthrough of an electrically insulating
material (3, 4) and a leadthrough pin (5, 6), which lid is sealed hermetically to
said box, a negative electrode of an alkali metal, a positive electrode and an electrolyte
which comprises a corrosive constituent. The cell lid has such a shape that a chamber
is formed which is sealed from the ambient. Both walls have a leadthrough of an electrically
insulating material and a leadthrough pin. |
[0001] The invention relates to a battery of one or more electrochemical cells comprising in a metal cell container having a metal cell lid with a leadthrough of an electrically insulating material and a leadthrough pin, which lid is sealed hermetically to said container, a negative electrode of an alkali metal, a positive electrode and an electrolyte which comprises a corrosive constituent.
[0002] A known battery of this type comprises one or more cells having a negative electrode of lithium, a positive electrode of nickel or carbon, and an electrolyte the solvent of which consists entirely or partly of thionyl chloride or another oxyhalide. The solvent may alternatively be an organic solvent. The solvent and/or the substances dissolved therein, for example, complexes of lithium salts, depolarizers such as halogen complexes, may have a corrosive influence on the leadthrough material. Leadthrough material may be, for example, glass, ceramic or an organic polymer material, for example teflon.
[0003] For a number of applications there is the need for batteries which have a guaranteed storage stabilits for a longer period of time, which can operate in a temperature range between approximately -40° C and +63° C, and which can be stored at temperatures between approximately -55°C and +72° C.
[0004] These requirements can be satisfied at any rate only by hermetically sealed cells. One of the problems with these cells is the corrosion of the leadthrough material by the electrolyte and/or the substances dissolved therein. This corrosion may be delayed by a suitable choice of the composition of the leadthrough material, but it cannot be suppressed entirely. Once the corrosion of the leadthrought material has made such a progress that the cell contents are in open communication with the atmosphere first via a capillary, the corrosion can make rapid progress. This is caused by the evaporation of the solvent and the capillar attraction of electrolyte into the capillary. If the solvent in itself is corrosive or comprises a corrosive constituent, electronic and electrical components in the surroundings of the battery can be corroded to such an extent that after some time they no longer operate in the desired manner. Moreover, the battery action decreases due to the loss of solvent (desiccation).
[0005] It is an object of the invention to achieve a prolonged life of batteries of the type mentioned in the opening paragraph.
[0006] According to the invention, this object is achieved by means of a battery of the type described which is characterized in that the cell lid has a double-walled construction in which a space which is sealed from the ambient is formed, both walls comprising a leadthrough of electrically insulating material and a leadthrough pin.
[0007] The invention is based on the recognition of the fact that if corrosion cannot be prevented definitely, an extension of life can nevertheless be reached by suppressing the capillary rising of the electrolyte in the capillary formed in the corrosion by producing above the capillary a vapour pressure of the electrolyte solvent which corresponds to the vapour pressure of the electrolyte solvent at the ambient temperature.
[0008] In the construction according to the invention this can be achieved by giving the cell lid with leadthrough a double-walled construction in which a chamber is formed which is sealed from the atmosphere.
[0009] The sealed chamber is preferably filled with a gas, for example, air, nitrogen or the like, which does not currode the metal of the cell lid. It has been found that a vapour pressure of the solvent need be built up only after the capillary has formed in the leadthrough between the chamber and the cell contents. Said vapour pressure is then built up by the electrolyte solvent itself seeping through the capillary.
[0010] According to another embodiment of the invention an electrolyte-absorbing and/or neutralizing material may be present in the chamber. The neutralizing material preferably consists of a substance which upon reaction with the electrolyte forms a gas, for example, ammonium carbonate and ammonium bicarbonate or an alkali carbonate or alkalibi carbonate. As a result of this an extra gas pressure is formed in the chamber which forces back the capillary rise of the electrolyte solvent.
[0011] The leadthrough provided in the double-walled lid may consist of various materials and combinations of materials. The specific advantages of a number of possible combinations will now be described.
- The wall of the cell lid which is in direct contact with the contents of the cell has a leadthrough of a synthetic resin material, the outer wall has a leadthrough of glass.
[0012] In a cell having an electrode of lithium corrosion by lithium cannot occur as is possible in a glass leadthrough under reduction the electric resistance. Such a reduction of the electric resistance in a glass leadthrough may lead to premature self-discharge.
[0013] The glass leadthrough in the outer wall, which leadthrough can better withstand great temperature differences, protects the whole cell system from external influences. Possible small leakages as a result of great temperature differences on the inner leadthrough will not have a great influence on the glass leadthrough of the outer wall because only very small quantities of electrolyte can leak away from the cell.
-Both walls of the lid have a leadthrough of a synthetic resin. The advantage of this construction is in particular that there is an ample choice of materials which may be used. The coefficient of expansion plays a less great role than in glass leadthroughs. This construction may be used while choosing the correct synthetic resins, both for batteries the electrolyte solvent of which is an organic solvent or is an oxyhalide.
- Both walls have a glass leadthrough. This construction as such is suitable for batteries which are stored for long periods of time. The storage time can even be extended by providing the glass leadthroughs with a protective layer (for example, a coating of a synthetic resin).
- The wall of the cell lid which is in direct contact with the contents of the cell has a glass leadthrough, the outer wall has a leadthrough of a synthetic resin.
[0014] Should a leakage occur in the glass leadthrough, the leadthrough of synthetic resin will prevent the electrolyt from running out into the ambient for a considerable period of time.
[0015] The glass for the glass leadthrough may consist, for example, of a calcium-barium glass, for example, the Corning glass 9010 of Corning Glassworks, U.S.A.
[0016] Where a glass leadthrough has been mentioned hereinbefore, a leadthrough of a ceramic material, for example, on the basis of aluminium oxide or a glass ceramic, may equally be used. As a synthetic resin for the leadthrough of synthetic resin may be used, for example, : high-density polyethylene and polypropylene, fluorocarbon polymers (for example polytetrafluoroethylene, polyvinylidene difluoride, copolymerisates of ethylene and tetrafluoroethylene), epoxy resins and phenylformaldehyde resins.
[0017] The invention will now be described in greater detail with reference to the accompanying drawing.
[0018] The Figures in the drawing are sectional views of a part of a cell with cover
Figure 1 with a leadthrough of synthetic resin and one of glass
Figure 2 with two leadthroughs of a synthetic resin
Figure 3 with two glass leadthroughs
Figure 4 with a leadthrough of glass and one of a synthetic resin.
[0020] Reference numeral 1 denotes a part of the cell wall on which a double-walled lid cover 2 has been sealed hermetically, for example, by welding. The leadthroughs are situated in the walls 2A and 2B, reference numeral 3 is always a leadthrough of a synthetic resin and reference numeral 4 a glass leadthrough. Reference numerals 5 and 6 denote the current leadthrough pins with connection wires 7. the connection wire 7 may comprise a narrowing or the like which may operate as a fuse. A glass leadthrough is to be understood to include a leadthrough of a ceramic material or a glass ceramic.
1. A battery of one or more electrochemical cells comprising in a metal cell box having
a cell lid with a leadthrough of an electrically insulating material and a leadthrough
pin, which lid is hermetically sealed to said box, a negative electrode of an alkali
metal, a positive electrode of an elektrolyte which comprises a corrosive constituent,
characterized in that the cell lid has a double-walled construction in which a chamber
is formed which is sealed from the ambient, both walls comprising a leadthrough of
an electrically insulating material and a leadthrough pin.
2. A battery as claimed in Claim 1, characterized in that the cell cover has a double-walled
construction in which a gas-filled chamber is formed which is sealed from the ambient.
3. A battery as claimed in Claim 1, characterized in that the chamber comprises an
electrolyte-absorbing and/or neutralising material.